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Guide

Cords, codes and power strips

The rules Cordwise uses, written out so you can check them.

How the codes work

Each cord gets a letter for its kind and a number in the order you listed it: P power (mains plugs and power bricks), V video (HDMI, DisplayPort), N network (Ethernet, coax), U USB, A audio, X anything else. So the first power cord is P1, the second P2, the first video cable V1. Keep the list in the same order and the codes stay the same.

Finding the watts

Look for the rating label on the device, the back of its power brick, or the manual. It shows either a watt figure (for example “65W”) or volts and amps: multiply them (120 V × 0.5 A = 60 W). For a brick, use the input side. The label gives the most a device may draw; most of the time it draws less, so the total Cordwise shows leans to the safe side.

Reading the load check

A strip’s rating in watts is its amps times 120 V in the US: a 15 A strip is 1,800 W. Cordwise calls a total up to 80% of that “comfortable”, above 80% “near the limit” and above 100% “over the rating”. The 80% margin follows the common rule of thumb for loads that run for hours: the US National Electrical Code sizes branch circuits at 125% of a continuous load, which is the same as keeping that load at 80% of the rating [1]. Heaters, kettles, hair dryers and space heaters belong in a wall outlet, not a strip [3].

  • Plug the strip straight into a wall outlet. Do not plug a strip into another strip or an extension cord [2].
  • A strip that is warm, discoloured, buzzing or smells of hot plastic should be unplugged and replaced.
  • The check is arithmetic on your numbers. It cannot see the wall wiring, other things on the same circuit, or a damaged cord.

Printing and fixing the labels

  1. Print at 100% (“Actual size”). Check the 1-inch square with a ruler.
  2. Cut each flag along its outline. Plain paper works; label paper or a strip of clear tape over the print makes it last.
  3. Wrap the middle band around the cord about 2 in from the plug, and press the two faces together with glue or tape.
  4. Every cord has two flags: one at the device end, one at the plug end. Each says where the other end goes.

Sources

  1. NFPA 70, National Electrical Code, sections 210.19(A)(1) and 210.20(A): branch-circuit conductors and overcurrent protection sized at no less than the non-continuous load plus 125% of the continuous load. Free read-only access at nfpa.org.
  2. NFPA 1, Fire Code, section 11.1.4 (relocatable power taps): a power strip is to be plugged directly into a permanently installed receptacle, not into another strip or an extension cord. nfpa.org.
  3. U.S. Fire Administration (FEMA), space heater safety: plug space heaters into a wall outlet, never into an extension cord or power strip. usfa.fema.gov.

Cordwise is not an electrician. For wiring, a warm outlet or a breaker that trips, call a licensed electrician.